1. Field of the Invention
The present invention relates to a data transmission system. More particularly, the present invention relates to a data transmission system to be used as a constituent of a network making it possible to transmit data among a plurality of asynchronous systems.
2. Description of the Related Art
As a conventional method for transmitting data among asynchronous system, first-in first-out (FIFO) memories are generally used as buffers among the systems. Such a transmission system is described for example in "Interface" Aug. 1984 pages 268 to 270.
FIGS. 1 and 2 are schematic block diagrams of conventional asynchronous data transmission systems. First referring to FIGS. 1 and 2, a conventional asynchronous data transmission system using FIFO memories will be described. As shown in FIG. 1, in the case of transmitting data from a system 11 operating asynchronously to a system 13 operating also asynchronously, a FIFO memory 12 is connected therebetween and this FIFO memory 12 is used as a buffer.
In addition, as shown in FIG. 2, in the case of connecting a plurality of asynchronous systems 14, 16, 18 and 20, FIFO memories 15, 17 and 19 are connected between the respective systems.
It is to be noted that a conventional FIFO memory has only a buffer function for data. As a result, if such FIFO memories are used to connect asynchronous systems, the asynchronous systems can only be connected serially as shown in FIGS. 1 and 2. Accordingly, the whole network system connected by such FIFO memories only forms a pipelining mechanism by simple cascade connection as shown in FIG. 2 and its flexibility is extremely limited.